1. Field of the Invention
This invention relates to the large-scale production of commercially pure hydrogen gas in general, and in particular, to a dense-phase flow splitter and high-velocity, two-phase injector for use in a one-step, two-particle, fluidized-bed, steam-and-methane reactor used for such production.
2. Related Art
Hydrogen is one of the more common elements found in nature, and is present in many fuels, often combined with carbon, and in a large number of other organic and inorganic compounds. Hydrogen is widely used for upgrading petroleum “feed stocks” to more useful products. Hydrogen is also used in many chemical reactions, such as in the reduction or synthesizing of compounds, and as a primary chemical reactant in the production of many useful commercial products, such as cyclohexane, ammonia, and methanol.
In addition to the above uses, hydrogen is also quickly gaining a reputation as an “environmentally friendly” fuel because it reduces so-called “greenhouse emissions.” In particular, hydrogen can drive a fuel cell to produce electricity, or can be used to produce a substantially “clean” source of electricity for powering industrial machines, automobiles, and other internal combustion-driven devices.
Hydrogen production systems include the recovery of hydrogen as a byproduct from various industrial processes, and the electrical decomposition of water. Presently, however, the most economical means is the removal of hydrogen from an existing organic compound. Several methods are known for removing or generating hydrogen from carbonaceous or hydrocarbon materials. And, although many hydrocarbon molecules can be “reformed” to liberate hydrogen atoms therefrom, the most commonly used is methane, or natural gas.
The use of hydrocarbons as hydrogen sources, or “feedstock” materials, has many inherent advantages. Hydrocarbon fuels are relatively common and sufficiently inexpensive to make large-scale hydrogen production from them economically feasible. Also, safe handling methods and transport mechanisms are sufficiently well-developed to enable safe and expeditious transport of the hydrocarbons for use in the different hydrogen reforming and other generation techniques.
Currently, the majority of commercial hydrogen production uses methane as a feedstock. Generally, steam-and-methane reformers, or “reactors,” are used on the methane in large-scale industrial processes to liberate a stream of hydrogen gas. The generation of hydrogen from natural gas via steam reforming is a well-established commercial process. However, these commercial units tend to be extremely large and subject to significant amounts of “methane slip,” i.e., methane feedstock that passes through the reformer unreacted. The presence of such methane (and other reactants or byproducts) serves to pollute the hydrogen, thereby rendering it unsuitable for most uses without further purification.
The disclosures in the above-referenced Related Applications detail the development by the Boeing Company of the “Boeing One Step Hydrogen” (“BOSH2”) process, which uses calcium oxide particles for the economical, large-scale production of hydrogen with yields that are both larger and purer than prior art processes. The BOSH2 process comprises a “two-particle,” fluidized-bed, steam reforming process that uses two types of solid particles: 1) Relatively large, porous particles of alumina (Al2O3) having a nickel (Ni) catalyst deposited on both their interior and exterior surfaces, for converting methane (CH4) to hydrogen (H2) via the reaction:CH4+H2O→3H2+CO2,and (2) relatively small calcium oxide (CaO) particles for converting the gaseous carbon dioxide (CO2) “byproduct” to solid calcium carbonate (CaCO3) via the reaction:CO2+CaO→CaCO3.
The fluidized bed reactor is operated so that the large alumina/nickel-catalyst particles remain within the fluidized bed at all times, while the smaller calcium oxide/carbonate particles are entrained with the gas and flow continuously through and out of the bed for subsequent separation and re-use of the calcium oxide CO2-adsorbent.
Significant economic advantages have been shown in the size, throughput, and single-pass conversion efficiencies when using the BOSH2 two-particle fluidized bed process in methane/steam reformer reactors described above. However, as this process has matured over time, certain technical issues have arisen that require resolution. One of these relates to the need for obtaining a very uniform distribution and rapid mixing of both the solid calcium oxide particles and the steam/methane gas mixture across the bottom of the fluidized catalyst bed of the reactor. Uniform splitting of entrained calcium-oxide-particle streams into multiple (i.e., on the order of 6 to 36) feed streams is problematic in dilute, two-phase pneumatic gas flows. The subsequent rapid mixing of these streams with the recirculating fluidized bed material is also important to prevent excessive hot spots within the bed, which could cause over-heating issues. This is because the reaction of the CO2 with the calcium oxide is highly exothermic, and can potentially lead to local, destructive “hot zones” if not accurately counterbalanced by the highly endothermic methane/steam reaction. Therefore, good, uniform dispersions of the methane, steam, and calcium oxide reactants with the contents of the bulk fluidized bed at or near the bed's injectors is necessary and important to ensure reliable reactor operation.